The native heart valves (i.e., the aortic, pulmonary, tricuspid and mitral valves) serve critical functions in assuring the forward flow of an adequate supply of blood ugh the cardiovascular system. These heart valves can be rendered less effective by congenital malformations, inflammatory processes, infectious conditions or disease.
Mitral valve regurgitation occurs when the posterior and anterior leaflets fail to fully close during systole. This enables blood to leak backward into the left atrium during contraction. The most common cause of mitral regurgitation is age-related connective tissue degeneration. Degenerative valve diseases occur at an annual incidence rate of 2-3% in industrialized nations. Mitral regurgitation may also be caused by cardiac ischemia, cardiac dilation/remodeling, Rheumatic fever, Marfan's syndrome, and other diseases and disorders.
Such damage to the valves can result in serious cardiovascular compromise or death. For many years the definitive treatment for such disorders was the surgical repair or replacement of the valve during open heart surgery. However, such surgeries are highly invasive and are prone to many complications. Therefore, elderly or frail patients with defective heart valves often go untreated.
Minimally invasive, transvascular techniques now enable surgeons to access cardiac valves without open-heart surgery. Catheters are inserted into vasculature at a site that is relatively distant from the heart. The catheters carry therapeutic devices through the patient's vasculature and to the malfunctioning heart valve. Once there, the devices are deployed within the valve to prevent further backflow of blood. For example, a transvascular technique has been developed for introducing and implanting a prosthetic heart valve using a flexible catheter in a manner that is much less invasive than open heart surgery. In this technique, a prosthetic valve is mounted in a crimped state on the end portion of a flexible catheter and advanced through a blood vessel of the patient until the valve reaches the implantation site. The valve at the catheter tip is then expanded to its functional size at the site of the defective native valve such as by inflating a balloon on which the valve is mounted.
Another known technique for implanting a prosthetic aortic valve is a transapical approach where a small incision is made in the chest wall of a patient and the catheter is advanced through the apex (e.g., bottom tip) of the heart. Transapical techniques are disclosed in U.S. Patent Application Publication No. 2007/0112422. Like the transvascular approach, the transapical approach can include a balloon catheter having a steering mechanism for delivering a balloon-expandable prosthetic heart valve through an introducer to the aortic annulus. The balloon catheter can include a deflecting segment just proximal to the distal balloon to facilitate positioning of the prosthetic heart valve in the proper orientation within the aortic annulus.
The above techniques and others have provided numerous options for high operative risk patients with aortic valve disease to avoid the consequences of open heart surgery and cardiopulmonary bypass. While devices and procedures for the aortic valve are well developed, such catheter-based procedures are not necessarily applicable to the mitral valve due to the distinct differences between the aortic and mitral valve. The mitral valve has a complex subvalvular apparatus, i.e., chordae tendinae, which are not present in the aortic valve.
Surgical mitral valve repair techniques (e.g., mitral annuloplasty) have increased in popularity due to their high success rates and clinical improvements noted after repair. In addition to the existing mitral valve repair technologies, there are a number of new technologies aimed at making mitral valve repair a less invasive procedure. These technologies range from iterations of the Alfieri stitch procedure to coronary sinus-based modifications of mitral anatomy to subvalvular applications or ventricular remodeling devices, which would incidentally correct mitral regurgitation.
However, for mitral valve replacement, few less-invasive options are available. There are approximately 25,000 mitral valve replacements (MVR) each year in the United States. However, it is estimated that over 300,000 patients who meet guidelines for treatment are denied treatment based on their age and/or co-morbidities. Thus, a need exists for minimally invasive techniques for replacing the mitral valve.